officina Meccanica Montenero of Italy has exhibited a fly comb with motion boxes fitted on both sides to achieve 3000 strokes per minute without vibration. Further the comb shaft is made of special alloy of having 50 per cent reduction in weight. This reduction of 50 percent of reduced weight, resulted in less wear and tear of parts, low vibration and energy consumption.
Roller doffing device
Increase of speeds of licker-in, cyliner and doffer for achieving higher production rate, demands corresponding increase of doffer comb speed to avoid the loading of fibres on the doffer.
But the doffer comb fails to remove the fibres from doffer when the speed exceeds 16 RPM. Therefore many doffing devices have been developed to cope up with high production.
Roller doffing devices are of the wing two types.
1. crossrollvarga 2. India rolvarga Roller doffing device.
crosrol varga unit
India rol varga unit.
one set of stripping roller and pair of crush roll unit is provided.
Two sets of stripping roll &
pair of crush roll units are linked together so that the IInd set of crush roll is able to do a fine purification of web.
Crosrolvarga and India Rolvarga Roller doffing device
Stripping roller strip the web from the doffer under positive control at any production rate. The web is removed from the stripper by redirecting Roller.
Both the stripping and Redirecting Roller are covered with a specially designed Metallic wires.
Now, the web is carried into the nip of the pair of polished crush rolls or pressure roller or web purifying roller.
The pressure Roller crush the impurities and extract the if rash from the web and apply draft to the web.
Total draft applied between the doffer and calender roller is app. 1. 4
This draft parallelizes the fibres giving better exposure of trash to the crushing action.
This amount of pressure applied by the crush roll can be varied according to the quality of cotton being processed and rate of production of card.
Both top and bottom crushing rollers are provided with adjustable & replaceable steel scraper blade which removes dust particles, impurities and seed bits from the crushing roll.
A spiral groove cut into the surface of each crosrol prevents the accumulation of fly under the blade.
For synthetic fibre-plain crush roll with nylon blade. is used & should not be given any pressure.
For coarser sliver - crush Roll pressure has to be increased.
From the crushroll, the web coming out is collected and
condensed by the apron web doffing device and passed through trumpet and calender Roller.
In India Rol varga unit, There is no redirecting roller web from 1st stripping roll is carried into the nip of 1st set of crush roll directly, a second stripping roller collects the web from the 1st set of crush roller.
From 2nd stripping roll the web is now carried into the nip of the pair of 2nd set of crush roller.
Any impurities, which may have been protected by the thick fibre layer when it is passed through the first pair of crush roller now, have the chance to be crushed and eliminated by the 2nd set of crush roll. Then only the web is condensed and passed through the trumpet & calender Roll.
Calender Rollers are mounted on ball bearing and top calender roll is provided with spring weighting.
Sliver break stop motion is incorporated in the calender Roller unit.
Advantages of Roller Doffing Unit.
Smooth auto doffing at any speed of doffer with absolute web control
Improved yarn quality by the reduction of impurities.
3 to 5 times more production than conventional card.
Consistent doffer speed which enables uniform production rate.
Upgrading of dirty cotton by ironing the web.
Higher efficiency and reduction of end breaks at spinning frame.
Setting points in India Rol unit:
Cylinder to doffer 0. 004 "
Doffer to stripping roller 0. 005"
Stripping roller to crush roller 0. 032"
Crush rol to 2nd stripping roller 0. 022"
2nd Stripping roller to second crush Roller"
Apron web doffing device
Apron web doffing device is used for effective controlling and doffing the web which is delivered from crush roller of roller doffing unit of HP card i. e., the web delivered from the crush roller is gathered by the cross apron as shown and condensed to form a sliver. It helps to cope up with very high delivery speeds like 300 metre per minute.
